TLR3 triggering regulates PD-L1 (CD274) expression in human neuroblastoma cells

• We report PD-L1 expression on human neuroblastoma cells.
• Our data show that TLR3 triggering and IFNγ exposure induce strong PD-L1 and HLA class I upregulation in neuroblastoma cells.
• The TLR3 ligand poly(I:C) inhibits endogenous TGFβ secretion and induces IL-8 release by human neuroblastoma cells.
• Simultaneous TLR3 stimulation and PD-L1 blockade in neuroblastoma cells increases immunogenicity and stimulates T-cells.
• We propose the combination of TLR3 stimulation with PD-L1 blockade as a new way to increase anti-neuroblastoma immunity.

Neuroblastoma is the most common extracranial solid tumor in children, causing 12% of all pediatric cancer mortality. Neuroblastoma specific T-cells have been detected in patients, but usually fail to attack and eradicate the tumors. Tumor immune evasion may thus play an important role in neuroblastoma pathogenicity. Recent research in adult cancer patients shows that targeting T-cell check-point molecules PD-1/PD-L1 (or CD279/CD274) may bolster immune reactivity against solid tumors. Also, infections can be associated with spontaneous neuroblastoma regression. In our current study, we therefore investigated if antibody targeting of PD-L1 and triggering of selective pathogen-receptor Toll-like receptors (TLRs) potentiates immunogenicity of neuroblastoma cells. We find this to be the case. TLR3 triggering induced strong upregulation of both MHC class I and PD-L1 on neuroblastoma cells. At the same time TGF-β levels decreased and IL-8 secretion was induced. The combined neuroblastoma cell treatment using PD-L1 blockade and TLR3 triggering using virus analog poly(I:C) moreover induced CD4+ and CD8+ T-cell activation. Thus, we propose combined treatment using PD-L1 blockade with synthetic TLR ligands as an avenue toward new immunotherapy against human neuroblastoma.